On Wednesday, Apple sent out an e-mail to developers alerting them that they should prepare for Safari Notifications, which will be a major feature of the upcoming OS X Mavericks, which is expected to be a major topic of discussion at Apple’s September 10th event next week.
With Safari Notifications, users will be able to receive push notifications from Web pages directly through Safari whether the Web browser is physically open or not. For example, breaking news from CNN could be displayed as notifications on the user's desktop, as shown above. Apple explains how the feature works on their Web site:
Originally Posted by Apple
Safari Notifications will be just one of the many features coming in OS X Mavericks. Other features to look forward to include native Maps and iBooks applications, as well as other useful features like Finder tabs, App Nap, and Compressed Memory.
Sources: Apple via Cult of Mac